This invention relates to an electrode assembly for a display apparatus, and more particularly to an electrode assembly capable of increasing accuracy in assembly and eliminating deficiencies in images.
The structure of a display apparatus on which our experiments have been carried out will first be explained. FIGS. 1 to 6 schematically show the display apparatus.
In FIG. 1, reference numeral 1 represents a fluorescent screen, 2 a cathode, 3 coupling spacers and 4 electrodes. An electron beam which has been emitted from the cathode 2 is subjected to horizontal and vertical deflection and luminance modulation by means of the various electrodes 4 and reaches the fluorescent screen 1 to cause light emission.
On the electrodes 4 are provided electron beam passage holes 8, 8' and 8", as shown in FIGS. 2, 3 and 4, such that the electron beam passes therethrough. The rigidity of the electrodes 4 varies depending on the configuration and the size of the electron beam passage holes 8, 8' and 8". For example, comparing the electrodes 5, 6 and 7 shown in FIGS. 2, 3 and 4, the ridigity in relation to tension and compression in the horizontal direction, as viewed in the Figures, is highest in the electrode 6, the rigidity of the electrode 5 being slightly lower than that of the electrode 6. This is because horizontal cleats 10' are continuous and vertical cleats 11' (clearance between two holes 8', 8') are wide in the electrode 6, which produces a stress flow in the cleats 11' with respect to tension and compression (in the horizontal direction), whereby the rigidity of the horizontal cleats 10' and the vertical cleats 11' are combined. In the electrode 5, however, although the horizontal cleats 10 are continuous, vertical cleats 11 are not so wide as that of the electrode 6 and are not wide enough to produce a stress flow, so that the rigidity is approximately equal to that of the horizontal cleats 10 which are naturally low in comparison with the electrode 6. Since in the electrode 7, there are no continuous horizontal cleats, the rigidity is extremely low as compared with the electrodes 5 and 6.
The coupling spacer 3 is essentially composed of a metal substrate 12 with an insulator 13 being attached thereto for the purpose of controlling the thickness and with a frit glass 14 for coupling being applied on the insulator 13.
The electrodes 4 are not joined and fixed until after all of the electrodes which constitute an electrode block have been completed. A unit is made by joining several electrodes 4 and by joining and fixing all the units constituting the block to complete, the final electrode block. This is because this method of joining the units can bring about higher accuracy in the block than the method of joining and fixing all the electrodes 4 at one time.
A method of making a unit of a part from electrodes 4 will next be explained. An example of joining and fixing electrodes 6 of the highest rigidity and electrodes 7 of the lowest ridigity through the coupling spacer 3 is illustrated in FIG. 6. At this time, each of the electrodes 6 and 7 must be positioned correctly in relation to each other, and it is also required that the dimensions a and b in FIG. 6 are equal and correspond with the printing pattern pitch (not shown) of the fluorescent screen 1.
The electron beam passes through a window portion W at right angles to the plane of the drawings, and since the electron beam is more sensitive to the positional accuracy of the electrodes in the horizontal direction (direction X), and, in terms of the printing pattern of the fluorescent screen 1, the electrodes should be positioned with greater precision in the horizontal direction than in the vertical direction (direction Y).
Positioning of each of the electrodes 5, 6 and 7 relative to one another is conducted by inserting pins (not shown) into locating holes 9, 9' and 9" which are formed with high accuracy in the electrodes 5, 6 and 7. The coupling spacers 3 function to insulate the electrodes 5, 6 and 7 from one another, and maintain spaces of, predetermined dimension therebetween.
It is possible to form an end block by joining and fixing the units formed in the above-described way by means of the coupling spacers 3 and the remaining electrode 4.
The above is a summary of the structure and the manufacturing method of the display apparatus.
The problems of accuracy in assembly which arise with the above-described structure and manufacturing method will now be described.
The frit glass 14 is calcined at a temperature of 400.degree.-500.degree. C. Since during heating, it is not hardened until the temperature is reached, thermal stress is not generated in the interior of each layer of the electrode block consisting of the electrodes 4 and the coupling spacers 3. At the time of cooling the frit glass has already been hardened and each electrode has been fixed by the coupling spacers 3, so that thermal stress is produced in the interior of each electrode 4 and each coupling spacer 3 (the metal substrate 12, the insulator 13 and the frit glass 14). As a result, the electrode block composed of joined and fixed electrodes warps in the direction Z, whereby the riding position of the electron beam on the fluorescent screen 1 deviates from its correct position and the screen presents a phenomenon of chromatic error. The reason why warp is produced on the electrode block is that, since the distribution of the thermal stress generated on each layer of the electrodes 4 and the coupling spacers 3 is out of balance in relation to the neutral axis of the electrode block, rotating moment is produced in relation to the neutral axis. The distribution and magnitude of the thermal stress produced on each layer of the electrodes 4 and the coupling spacers 3 is determined by the material constant thereof (rate of thermal expansion, rigidity, plate thickness or the like).
A conventional electrode block is composed of electrodes 6, 7, 6, 6, 7, 5, which are disposed in that order in the direction from the cathode 2, one coupling spacer 3 being disposed between adjadent electrodes 4 with the proviso that two coupling spacers 3 are inserted between the third electrode 6 and the fourth electrode 6 from the cathode 2. The structure of each electrode 4 of this electrode block is determined under the state wherein focusing of the electron beam on the fluorescent screen is optimum, and due to a large difference in ridigity between the electrode 6 closest to the cathode 2 and the electrode 7 closest to the fluorescent screen 1, this structure is far from symmetrical in relation to the neutral axis of the electrode block.
Though the positional accuracy is required to be .+-.10 .mu.m (+ means that the electrode block warps such to be convex relative to the fluorescent screen 1, and - indicates the reverse) in the last stage of coupling units, by virtue of the above-described phenomena an accuracy of only about .+-.200 .mu.m has often been obtained.